This invention relates to a developing method of electrostatic latent images for full color image formation.
Electrophotographic methods are widely used in PPC, printers, facsimiles and the like. A full color image formation methods which reproduce multicolor by laminating plural kinds of color toners have been used.
A developing method excellent in developing characteristics is required in these full color developing methods since the methods are mainly used for copying the manuscripts containing pictures, photographs, graphics and the like. In such a developing method, a bias voltage with an alternating current component superposed on a direct current component is applied on a developer retaining member that retains and transfers the developer.
Because the developer is vibrated and stirred more strongly in the development area by the superposed alternating current component, a toner lowly charged or heterogeneously charged is liable to be scattered by a vibration phenomenon, resulting in toner fogs or toner dirts of the interior of the apparatus by the toner. Therefore, a toner with homogeneous and appropriate amount of electrostatic charge should be supplied to the developing method. One possible method for solving the problem is to add a charge controlling agent suppressing agent to the toner. The agents having excellent characteristics for controlling the electrostatic charge are, however, usually colored, and can not be used in the full color toner. The problem of chargeability is, therefore, has not yet been settled enough.
Polyester resins with low viscosity are used for a binder resin for full color toner because of security of light-transmittance and adhesive properties among multilayers of copied images. The polyester resins, however, have some problems arising from their properties. For example, so called spent phenomenon of the toner in which the toner adheres to the surface of the carrier is liable to occur because of low viscosity of the binder resin for the toner. The spent toner is particularly liable to occur in the developing method in which an alternative current component is superposed on a direct current component, since a stress will be generated between the toner and the carrier by a vibration phenomenon.
While a fluidizing agent is added in a developer to improve fluidity, the agent is buried into a toner when viscosity of the toner is low. The fluidity is deteriorated. There is also another problem that characteristics of the toner varies largely by the environment because the polyester resins have --OH and/or --COOH groups in their molecular terminals.